Bye, Bye, Diesel: Mazda's United SportsCar Prototype Is Getting GassyStef Schrader6/19/15 5:04pm705EditPromoteGo to permalinkWe loved the Mazda6 Diesel race car that started off in Grand Am’s class for alternative fuels. It’s a diesel! So weird and quirky! Yeah! We even loved hearing that the diesel engine would live on in a United SportsCar P2 prototype. Unfortunately, that P2 has just been slow, so it’s time for a gas-powered engine swap.